The present invention relates to a direct smelting vessel for producing molten metal (which term includes metal alloys) from a metalliferous feed material such as ores and partly reduced ores.
The present invention relates particularly to a vessel that can be used for molten bath-based direct smelting processes.
The term xe2x80x9csmeltingxe2x80x9d is understood herein to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce liquid metal.
The term xe2x80x9cdirect smelting processxe2x80x9d is understood herein to mean a process that produces a molten metal directly from a metalliferous feed material, such as iron ore and partly reduced iron ore.
The present invention relates particularly to off-gas ducts for direct smelting vessels.
An object of the present invention is to provide an off-gas duct which minimises loss of molten material and solids entrained with off-gas.
According to the present invention there is provided a direct smelting vessel which is adapted to contain a molten bath of metal and slag and includes: a hearth; side walls that extend upwardly from the hearth; a roof; and an off-gas duct extending from an upper section of the vessel for discharging from the vessel an off-gas that is produced during a direct smelting process operated in the vessel, which off-gas duct includes:
(a) a first section which has a relatively slight upward inclination to the horizontal from an inlet end of the first section; and
(b) a second section which extends upwardly from an upper end of the first section at a relatively steep inclination to the horizontal.
In use, off-gas is forced to undergo a substantial change in direction in order to enter the first section. It is believed that, as a consequence, molten material and solids that are entrained in the off-gas contact and deposit one: (i) walls of the vessel that are at or in the region of the inlet end; and (ii) walls (particularly upper walls) of the first section at or in the region of the inlet end; and thereby separate from the off-gas. Molten material and solids that deposit on these walls move downwardly into the vessel.
In addition, in use, off-gas flowing along the first section is forced to undergo a substantial change of direction at the end of the first section in order to flow into the second section. Consequently, molten material and solids that are entrained in the off-gas tend to contact and deposit on the upwardly extending wall that is at the end of the first section and separate from the off-gas. It is believed that in this region of the duct, molten material either remains molten or solidifies on the wall. Molten material that remains molten flows downwardly into the first section and then along the first section into the vessel. Molten material that solidifies builds-up on the wall and with deposited solids eventually spalls and falls down into the first section. In view of the relatively higher temperature conditions in the first section the solidified material melts and flows back into the vessel or otherwise is carried by molten material back into the vessel.
The slightly inclined first section avoids the potentially serious problem of solid accretions falling back into the vessel and damaging equipment such as lances/tuyeres while a direct smelting process is being operated in the vessel or after a shut down. Such fall back is also a potentially serious safety issue for persons carrying out maintenance work in the vessel during a shut down.
Preferably the first section is formed having regard to operating conditions in the vessel so that at least a substantial part of the molten material that enters the first section with the off-gas is molten at the end of the slightly inclined first section. This feature ensures that there is minimal built-up of solid accretions in the first section.
More preferably in this regard the first section is formed so that the temperature drop along the length of the first section is less than 100xc2x0 C. and the overall temperature is maintained above the melting points of the molten material.
Preferably the amount of entrained material (molten and solids) in the off-gas discharged from the second section is less than 15 g, more preferably less than 10 g, per Nm3 off-gas.
Preferably the relatively slight upward inclination of the first section is less than 30xc2x0, more preferably less than 20xc2x0, to the horizontal.
It is preferred particularly that the angle of inclination be less than 10xc2x0.
Preferably the relatively steep inclination of the second section is 80-90xc2x0 to the horizontal.
Preferably the vessel includes a dead end bend that connects the first and second sections.
Preferably the dead end bend includes an access port in the dead end.
Preferably the vessel includes an off-gas chamber extending upwardly from the roof and the first section of the off-gas duct extends from the off-gas chamber.
Preferably the first section of the off-gas duct extends from a side wall of the off-gas chamber.
Preferably the ratio of the length of the first section to the minimum width dimension of the first section is at least 2:1, where the length of the first section is measured between the intersection of centrelines of the first and second sections and the intersections of the centreline of the first section and a vertical line through the inlet end of the first section. In a situation where there is an off-gas chamber and the first section extends from a side wall of the chamber the intersection of the centreline of the first section and a vertical centreline of the off-gas chamber is the measurement point at the inlet end of the first section.
Typically, the first and second sections are cylindrical and the minimum width dimension of the first section referred to in the preceding paragraph is the diameter of the first section.
Preferably the second section is formed so that the temperature drop along the length of the second section is sufficient to solidify at least a substantial part of any molten material that is in off-gas flowing through the second section before the off-gas reaches the end of the second section. This ensures that there is minimal, if any, carry over of molten material into downstream off-gas processing apparatus, such as hot cyclones and hot scrubbers, that may be affected adversely by molten material in off-gas.
Preferably the off-gas chamber is located centrally.
Preferably the vessel includes at least one lance for injecting oxygen-containing gas into the vessel which extends downwardly through the off-gas chamber into the vessel.
Preferably the ratio of the minimum width dimensions of the side walls of the vessel and the off-gas chamber is at least 1.5:1. In situations where the oxygen-containing gas injection lance or lances extend downwardly through the off-gas chamber, preferably the ratio is 1.5:1 to 2:1. In situations where the gas injection lance or lances are not located to extend through the off-gas chamber the ratio of minimum width dimensions may be up to 4:1.
Preferably the roof is upwardly inclined from the side walls at an angle in the range of 30 to 50xc2x0 to a horizontal axis (ie an included angle of 120 to 130xc2x0 measured between the side walls and the roof).
Preferably the angle of inclination is 40xc2x0 to the horizontal axis.
Preferably the side walls are cylindrical and the roof is frusto-conical and extends from an upper end of the side walls and terminates in the off-gas chamber.
Preferably the minimum width dimension of the side walls of the vessel is 8 meters.
According to the present invention there is also provided a direct smelting process operated in the above-described vessel.